Regularities of Cu, Pb and Zn adsorption by chernozems of the South of Russia

The parameters of Cu2+, Pb2+ and Zn2+ adsorption by chernozems of the south of Russia and their particle-size fractions were studied. The adsorption capacity of chernozems for Cu2+, Pb2+, and Zn2+ depending on the particle-size distribution decreased in the following sequence: clay loamy ordinary chernozem ~ clay loamy southern chernozem > loamy southern chernozem > loamy sandy southern chernozem. According to the parameters of the adsorption by the different particle-size fractions (Cmax and k), the heavy metal cations form a sequence analogous to that obtained for the entire soils: Cu2+ ≥ Pb2+ > Zn2+. The parameters of the heavy metal adsorption by similar particle-size fractions separated from different soils decreased in the following order: clay loamy chernozem > loamy chernozem > loamy sandy chernozem. The ratio between the content of exchangeable cations displaced from the soil adsorbing complex (SAC) into the solution and the content of adsorbed HMs decreased with the increasing concentration of adsorbed HMs. These values could be higher (for Cu2+ and Pb2+), equal, or lower than 1 (for Zn2+) and depend on the properties of HMs. At the first case, this was due to the dissolution of readily soluble salts at low HM concentrations in the SAC. In the latter case, this was related to the adsorption of associated forms HMs and the formation of new phases localized on the surface of soil particles at high HM concentrations in the SAC